Such arrangement will hereinafter be called a tribological arrangement. Examples of tribological arrangements are sets of gears and bearings. Further examples are belt chains, plane and roller bearings, linear bearings, sleeve bearings, pulleys, sliding plates and other similar devices which have long been used to transmit, communicate, or facilitate motion and power in mechanical devices.
In many cases, metal parts are used in tribological arrangements. Parts having polymeric contacting surfaces form an attractive alternative offering one or more of the following advantages: greater shock and vibration dampening, reduced weight, enhanced corrosion protection, reduced running noise, decreased power and maintenance use, and more freedom of component design. These advantages are especially important in applications such as printers, copying machines and household appliances, such as shaving apparatus and video apparatus. The polymers often used in tribological arrangements are nylon and polyacetal. However, tribological arrangements made of such polymer show less good wear, i.e. the amount of material worn off relative to the force applied to the material. This means that the arrangements have an arc relatively short life time.
It would be desirable if the parts of the arrangement would be amenable to machining or processing. A further requirement is that the material properly holds a tolerance, is able to withstand the torsional stresses of start-up and shut-down, and from cyclical fatigue.
Problems can result in a failure of the tooth from excessive wear which can be compounded by plastic flow or creep due to thermal softening. Additionally, tooth bending fatigue, contact fatigue (pitting and spalling), thermal fatigue, tooth bending impact, tooth shear, tooth shear, tooth clipping, case crushing, torsional shear, and stress ruptures have similar impact. The role of material selection and preparation thus clearly have much to do with the successful design of a motion and power transmission strategy. Low heat resistance, large thermal deformation, large shrinkage upon processing, and mediocre mechanical strength have precluded the use of numerous thermoplastics, thermosets, and resins from serious consideration in demanding applications.
While these considerations clearly apply to the structure and manufacture of gears, it should also be borne in mind that almost any device used to transmit, communicate, or facilitate power and motion necessarily involves similar concerns. For example, cams are generally used to communicate motion and power by means of a connection between an edge (or a groove therein) or surface and a follower. In addition to repetitive/cyclic movement and imposition of force acting on both cam and follower, these mechanisms are often designed to - incorporate large accelerations. Thus, the use of materials which cannot hold a tolerance (e.g., through loss of material) or which are not amenable to precision processing or manufacture can easily result in wildly eccentric motion and, ultimately, failure. It is therefore important to employ materials which can be worked to precision, which function well when placed in communication with each other, and which can withstand repetitive/cyclic movement and impact.
The same can be said of bearings with rolling or sliding contact. The repetitive and cyclic facilitation of motion inevitably raises concerns analogous to those of gears and cams.
Indeed, one skilled in the art will readily appreciate that from a materials perspective, an improvement in a means for transmitting power and motion is generally applicable to all means of power and motion transmission.
Rolling contact and sliding contact are manifested in most power and motion gear applications. Rolling contact predominates in motion and power transmission when such applications are between parallel shafts or between intersecting shafts. When non-parallel and non-inter- secting shafts are employed, sliding contact predominates. Thus, materials useful in power and motion transmission between all shaft set-ups exhibit both good wear and good strength.